The winter flocking behavior and breeding ecology of the Black-throated Sparrow (Amphispiza bilineata) were studied on 80 ha of creosotebush (Larrea divaricata) desertscrub, 40 km north of Las Cruces, Dona Ana County, New Mexico, from November 1976 through September 1977. The objective of the study was to examine the ecology of this abundant, but little studied, species and relate these data to its succes in its harsh desert habitats....Physiological and behavioral responses to deserts are discussed. It is suggested that four aspects of the ecology of Black-throated Sparrows are primarily responsible for its success in arid habitats: a) efficient physiological adaptations to desert environments, b) opportunism in foraging, c) fine-grained use of its habitat, and d) large territory to reduce predation through dispersion of nests.